Collapsibility of gypseous soil under suction control

Abstract

Many geotechnical problems and foundation failures in engineering structures were recorded due to the presence of unsaturated gypseous soils. One of the main reasons, which introduced large volume change and collapse behaviour is the variation of suction pressure and water potential within the gypseous soil mass. In this study, Sandy gypseous soil from Al-Ramadi city (west of Iraq) with gypsum content of more than 70 % is used. In order to investigate the collapse deformation of gypseous soil under suction control by multi-steps wetting procedure, also the effect of sensors positions and applied vertical stress, a special soil-model device is designed and manufactured. In this device, high accurate and sensitive Tensiometers and Time Domain Reflectometry (TDR) sensors with an assistance of high quality Data logger are used for measuring and monitoring of matric suction and gravimetric water content of the soil sample during the deformation processes. The test results indicated that a large volume change and collapse deformation occurred upon reduction of matric suction. The void ratio dramatically reduced stepwise with reducing of matric suction by multi-steps wetting irrespective the value of applied vertical stress.